Surfactant Self‐Assembly Enhances Tribopositivity of Stretchable Ionic Conductors for Wearable Energy Harvesting and Motion Sensing

• Published in: Advanced materials (Weinheim) 2024-08, Vol.36 (32), p.e2403905-n/a
• Main Authors: Bo, Xiangkun, Zhao, Hong, Valencia, Agnes, Liu, Fei, Li, Weilu, Daoud, Walid A.
• Format: Article
• Language: English
• Subjects: Alkali metals; Charge density; Charge materials; Conductors; Electrodes; Energy harvesting; Fluorine; Functional groups; Human motion; ionic conductor; Kinetic energy; Nanogenerators; Permittivity; Polyurethane resins; Self-assembly; Stretchability; surfactant self‐assembly; Surfactants; tribopositivity; Wearable technology
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.202403905

Boosting stretchability and electric output is critical for high‐performance wearable triboelectric nanogenerators (TENG). Herein, for the first time, a new approach for tuning the composition of surface functional groups through surfactant self‐assembly to improve the tribopositivity, where the assembly increases the transferred charge density and the relative permittivity of water polyurethane (WPU). Incorporating bis(trifluoromethanesulfonyl)imide (TFSI−) and alkali metal ions into a mixture of WPU and the surfactant forms a stretchable film that simultaneously functions as positive tribolayer and electrode, preventing the conventional detachment of tribolayer and electrode in long term usage. Further, the conductivity of the crosslinked film reaches 3.3 × 10−3 mS cm−1 while the elongation at break reaches 362%. Moreover, the surfactant self‐assembly impedes the adverse impact of the fluorine‐containing groups on tribopositivity. Consequently, the charge density reaches 155 µC m−2, being the highest recorded for WPU and stretchable ionic conductor based TENG. This work introduces a novel approach for boosting the output charge density while avoiding the adverse effect of ionic salts in solid conductors through a universal surfactant self‐assembly strategy, which can be extended to other materials. Further, the device is used to monitor and harvest the kinetic energy of human body motion. A surfactant self‐assembled stretchable solid‐state water polyurethane (WPU), which avoids the negative impact of high salt dissociation, is developed. Compared to pristine WPU, the surfactant self‐assembled WPU exhibits high ionic conductivity, relative permittivity, and tribopositivity. The fabricated device shows high electric output and can be efficiently employed in wearable electronics.